Sex-specific-evaluation of metabolic syndrome prevalence in Algeria: insights from the 2016–2017 non-communicable diseases risk factors survey

Metabolic syndrome (MetS) is a core driver of cardiovascular diseases (CVD); however, to date, gender differences in MetS prevalence and its components have not been assessed in the Algerian adult general population. This study aimed to determine the gender differences in MetS prevalence and its components, in the general population of Algeria. Secondary analysis was performed on data from the Algerian 2016–2017 non-communicable disease risk factor survey. MetS was determined according to the harmonized Joint Interim Statement criteria. A Poisson regression model based on Generalised Estimating Equations was used to estimate the adjusted prevalence ratios (aPR) for the sex-specific factors associated with MetS. Overall, the prevalence of MetS was 34.0% (95% CI 32.4–35.6). MetS prevalence in women and men was 39.1% (95% CI 37.0–41.3) and 29.1% (95% CI 27.2–31.2), respectively. The most frequent triad was the clustering of abdominal obesity with low HDL-cholesterol and high blood pressure among women (8.9%; 95% CI [8.0–10.0]) and low HDL-cholesterol with high blood pressure and hyperglycaemia among men (5.2%; 95% CI [4.3–6.3]). Increasing age (aPR 3.21 [2.35–4.39] in men and aPR 3.47 [2.86–4.22] in women), cohabitation (aPR 1.14 [1.05–1.24]), women residing in urban areas (aPR 1.13 [1.01–1.26]), men with higher educational levels (aPR 1.39 [1.14–1.70]), and men with insufficient physical activity (aPR 1.16 [1.05–1.30]) were associated with higher risk of MetS. In this population-based study, one in three Algerian adults had MetS, and key components including abdominal obesity, low HDL-cholesterol, and high blood pressure, are very common, especially in women. Reinforcing interventions for weight management targeting married women living in urban areas and improving sufficient physical activity in men with higher socioeconomic status could provide maximal health gains and stem the CVD epidemic in Algeria.


Data source and study population
This study used data from the Algerian STEPwise approach to Non-Communicable Disease (NCDs) risk factor surveillance (STEPS) survey, implemented by the Ministry of Health with the support of the WHO.STEPS is a WHO-recommended household-based survey for countries to obtain core data on the established risk factors that determine the major burden of NCDs.Two STEPS surveys have been conducted in Algeria (2003 and 2016-17), and the study protocols were approved by the National Council for the Ethics of Health Sciences review board.These cross-sectional surveys were carried out in compliance with the guidelines and regulations of the Helsinki Declaration, and written informed consent was obtained from all participants.Detailed study protocols, including the data collection methods have been published elsewhere 18,19 .
Briefly, the STEPS covers three different steps of risk factor assessment including home interviews, physical measurements, and biochemical measurements.For each survey, a multi-stage cluster sampling design was used to obtain representative data.The first stage of the sampling process involved the selection of primary sampling units (districts) followed by the selection of specific enumeration areas within these districts that contain a cluster of households.In the third stage, specific households within these enumeration areas were identified, and one individual within the age range of the survey was selected per household.Analysis weights were used to adjust the data so that it is representative of the target population.These weights were calculated by taking the inverse of the probability of selection of each participant and adjusted for differences in the age-sex composition of the sample population as compared to the target population.Different weight variables were used for each step of the survey to allow for differences in weight calculation due to participant refusal or drop out 19 .
For the present study, secondary analysis was conducted on data obtained from the second STEPS survey (2016-2017) and included adults aged 18-69 years who had undergone home interviews, physical measurements, and biochemical measurements.Pregnant women and those with established CVD were excluded from the study.A total of 6989 adults participated in the survey, and the overall response rate was 93.8%.Overall, 5719 adults were eligible and had no missing data for any of the five MetS components (Fig. 1).

Data collection and measures
In this survey, all 3 levels of risk factor assessment were performed.Sociodemographic data (including age, sex, level of education, work status, and place of residence) and behavioural information (tobacco use, healthy diet, and physical activity) were collected in step 1.In the second step, weight, height, waist circumference (WC), and blood pressure measurements were collected, whereas biochemical measurements to assess blood cholesterol and sugar levels were done in step 3. Details of the data collection procedure have been previously described 18 .Briefly, after at least 10 min of rest, the blood pressure of each participant was measured three times in a seated position, 5 min apart, and the mean value of the second and third readings was considered as the participant's blood pressure.A portable constant tape (precision of 0.1 cm) was used to measure height and WC in a standing position whilst weight was measured using a digital scale and recorded to the nearest 0.1 kg (kg).Body mass index (BMI) was calculated as the weight in kg divided by the height in square meters.Finally, fasting venous blood samples were obtained from each participant after an overnight fast to assess fasting plasma glucose (FPG) and blood lipids via the enzymatic colorimetric method.

Definition of MetS and variables
The harmonized MetS definition from the Joint Interim Statement 5 was used which constitutes the presence of any 3 of 5 risk factors including: central obesity, hypertension or antihypertensive drug treatment, elevated FPG or drug treatment for elevated glucose, elevated serum triglyceride or drug treatment for elevated triglyceride, and low HDL-cholesterol or drug treatment for reduced HDL-cholesterol (Table 1).Waist circumference for central obesity measurement was defined according to the Middle Eastern and Mediterranean population thresholds for men and women, whilst physical activity levels and daily fruit and vegetable consumption were assessed using the WHO guidelines 20 (Table 1).

Data processing and analysis
Statistical analyses were performed using STATA version 17.0.For descriptive statistics, categorical variables were summarised as frequencies and proportions, and the estimates accounted for the complex nature of the survey design using the different sampling weights.
To evaluate the association between MetS (as an outcome, using the harmonized criteria) and the individual sociodemographic (age, level of education, living status, occupation, and place of residence) and behavioural factors (smoking, physical activity, and fruit and vegetable consumption) crude and adjusted prevalence ratios (aPR) were estimated.First, univariable Poisson regression models based on Generalized Estimating Equations with robust standard errors and clustering by primary sampling unit to estimate crude prevalence ratios (cPR) and its 95% confidence intervals (CIs) were used 21,22 .
Multivariable analysis was performed and adjusted for individual covariates, and the adjusted prevalence ratio (aPR), 95% CI, and P-values were generated to determine the sex-specific predictors of MetS and its components in Algeria.A statistical significance was set at P < 0.05.
Reporting was performed according to Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines for cross-sectional studies.

Results
Overall, 6989 participants were included, of whom three out of four adults met the eligibility criteria.Therefore, 2547 men and 3172 women were included in the final analysis (Fig. 1).Table 2 summarises the baseline characteristics of the study population according to sex.The mean age of the study population was 38.2 ± 12.4 years, and more than two-thirds of the participants cohabited.Most people were unemployed, lived in urban areas, and had insufficient levels of daily fruit and vegetable consumption (Table 2).).Regarding the other MetS components, the prevalence of hyperglycaemia and hypertriglyceridemia was 33.6% (95% CI 31.0-36.4)and 13.5% (95% CI 12.3-14.9),respectively, in women, and 31.6%(95% CI 29.1-34.3)and 18.6% (95% CI 17.0-20.3),respectively, in men (Fig. 2).Table 3 shows the sex-specific prevalence of co-occurrence of MetS components.Overall, the most common triad was low HDL cholesterol, high blood pressure, and hyperglycaemia (6.7%; 95% CI 5.9-7.6),followed by abdominal obesity, low HDL cholesterol, and high blood pressure (6.6%; 95% CI 6.0-7.3),regardless of sex.None of the participants had more than four MetS components.; P = 0.023) higher MetS prevalence than those living in rural areas, and men who had a higher level of education had a MetS prevalence that was approximately 1.3-times higher (aPR 1.34 [1.11-1.61];P = 0.015) than those without formal education.Insufficient physical activity was the only behavioural factor associated with MetS in this population, and this association was observed only in men.Men who did not engage in sufficient levels of physical activity had about a 1.2-times higher (aPR1.16[1.05-1.30];P = 0.005) MetS prevalence than their physically active counterparts (Table 4).

Discussion
To the best of our knowledge, this is the first nationwide study on MetS prevalence and MetS individual components in Algeria, according to the harmonized diagnostic criteria.Overall, MetS prevalence in Algeria was 34.0%.This prevalence was higher in women than in men and tended to be significantly associated with increasing age, cohabitation, women residing in urban areas, and men with higher levels of education and insufficient physical activity levels.Regardless of sex, abdominal obesity and low HDL-cholesterol were the most frequent metabolic disorders, whereas the clustering of low HDL-cholesterol, high blood pressure, and hyperglycaemia was the most prevalent MetS combination.Women were more likely to have abdominal obesity or low HDL-cholesterol levels, whereas men were more likely to have hypertriglyceridemia.The estimated MetS prevalence was alarmingly high in Algeria, and there was comparable variation across the different definitions of MetS prevalence reported in the Eastern Mediterranean Region (EMR) and European populations.In the EMR, the estimated MetS prevalence according to the NCEP ATP III and IDF criteria was 32.9% and 34.6%, respectively, whereas the observed rates in Europe were 25.3% and 31.5%,respectively 6 .Our results were significantly higher than the pooled global MetS prevalence (12.5% [ATP III] and 28.2% [IDF]) 6 , the prevalence in SSA (17.1% [ATP III] and 18.0% [IDF]) 9 , and the prevalence in rural Algeria (17.4% [ATP III] and 25.7% [IDF]) 14 .This increase in prevalence is due to the ongoing epidemiological transition occurring with rapid economic growth, wherein unhealthy lifestyles such as physical inactivity and unhealthy diets are increasingly common as part of the ongoing cultural globalisation 23 .Other factors specific to the Algerian population could account for the variation in MetS prevalence.
Our data showed a higher MetS prevalence in women than that in men.This could be a result of the high prevalence of abdominal obesity and low HDL-cholesterol levels (Fig. 2).In fact, central obesity and low HDL cholesterol, which are key predictors of MetS, have been shown to be generally higher in African women than in African men 24 25 .Other potential explanations for the higher MetS prevalence in women could be due to a longer life expectancy compared to men 26 and because women are more prone than men to developing MetS in response to low socioeconomic status and work stress 27 .Moreover, recent observations indicate that men respond better than women to non-pharmaceutical strategies involving lifestyle measures and weight loss aimed at reducing MetS prevalence 28,29 .Comparable research in SSA 9 , African-American populations 30 , and Chinese populations 31 showed a higher MetS prevalence in women than in men, which is consistent with our findings.In contrast, MetS prevalence was higher in men than in women in the general European population 32,33 .The alarmingly high MetS prevalence in both men and women in our study mirrors the limited progress toward achieving diet-related NCD targets in Algeria, where 38.6% of adult women and 23.3% of adult men live with obesity 25 .
As expected, MetS prevalence increased with increasing age, regardless of sex.Individuals aged 45 years and older were three times more likely to have MetS than younger adults aged 18-29 years.This clustering pattern suggests that MetS in young people may differ from that in older individuals, with differing prognostic and treatment implications given that many individuals develop metabolic risk factors by the time they are 65 years or older 34 .Our results were similar to those of studies that demonstrated that the effect of clustering MetS components increased with age 31,[35][36][37] .In contrast, some studies have reported a levelling off in the rise of MetS prevalence with age, possibly due to a survivor effect whereby there is a relatively earlier death of young participants with MetS, causing a fall in prevalence in old age 38 .
Our analysis showed a positive association between MetS and cohabiting individuals, women in urban areas, men with higher levels of education, and men with low levels of physical activity.No association was found between occupation and insufficient fruit or vegetable intake.Socioeconomic disparities between men and women have been shown to be associated with different MetS prevalence rates.For instance, our findings are similar to those of the adult population of Saudi Arabia, where MetS had a positive association with income and higher education in men and unemployment in women 27 .In contrast, among Korean adults, men with the lowest education level, manual labourers, and those who were economically inactive were more likely to have MetS 39 .The higher likelihood of developing MetS in urban women in Algeria is probably a result of increased energy intake and reduced physical activity associated with urbanisation and cultural globalisation, which contribute to high obesity rates 40 .A higher MetS prevalence in urban areas has also been reported in SSA 9 , India 41 , and China 42 .In contrast, a study in the US reported a higher MetS prevalence in rural women 43 .This is possibly because the ongoing epidemiological transition has been experienced for longer in the US than in Algeria.Thus, it could be postulated that urban and rural differences in MetS in Algeria may disappear, and major efforts should not be made to reverse the disastrous lifestyle changes which have already occurred in urban areas.

Figure 2 .
Figure 2. Prevalence of MetS components in the Algerian general adult population.

Table 1 .
Definition of MetS components and behavioural factors.

associated with MetS in Algeria Tables
4presents the sex-specific determinants of MetS in Algeria.In both men and women, after adjusting for all other variables, increasing age was significantly associated with MetS.Compared with younger adults (age 18-29 years), MetS prevalence was three times higher among individuals aged 60-70 years (aPR 3.21[2.35-4.39];P< 0.001 in men, and aPR 3.47 [2.86-4.22];P< 0.001 in women, respectively).Living status was also significantly associated with MetS regardless of sex, whereas being married or cohabiting increased the risk of MetS by approximately 33% (aPR 1.33 [1.07-1.63];P= 0.009).Women who resided in urban areas had a 1.13-times (aPR 1.13[1.02-1.26]